U.S. Pat. No. 4,663,725, which is assigned to the same assignee as the present application, discloses the use of microprocessor based transport refrigeration control for use with a refrigerated container, with the refrigerant compressor being driven by an electric motor. This patent is directed primarily to the use of a microprocessor to operate the various components of the refrigeration system according to predetermined algorithms, and to detect and record faults which occur during the operation thereof.
U.S. Pat. No. 4,918,932, which is assigned to the same assignee as the present application, discloses the use of a microprocessor to determine average error between an operator selected set point temperature and the temperature of a space to be conditioned, using the outputs of return air and discharge air sensors, and the use of the average error in the determination of an error signal which modulates the capacity of the system.
Our U.S. Pat. No. 5,140,825, which is assigned to the same assignee as the present application, discloses a method which checks electrical components and wiring of a microprocessor controlled refrigeration system by using a battery and a current shunt which measures battery current. All checking is accomplished with a refrigerant prime mover off, so that an alternator driven thereby will not affect battery draw current. Each electrical component to be checked is automatically successively connected and disconnected from the battery, the current draw is compared with appropriate current draw limits, and an alarm is provided when the current draw is outside the draw limits.
It would be desirable, and it is an object of the invention to be able to monitor current draw of a refrigeration unit while it is operating, which, along with the teachings in our aforesaid patent, will provide complete protection for a refrigeration unit.
Refrigeration control systems of which we are aware utilize circuit breakers and fuses to isolate faulty components. Circuit breakers and fuses often result in unnecessarily shutting down the associated refrigeration unit when it is still capable of preserving a conditioned load, and circuit breakers and fuses add component and assembly cost to a refrigeration unit. It would be desirable, and it is another object of the present invention, to eliminate the need for circuit breakers and fuses in critical control areas of a refrigeration system.